Arc spray guns are well known in the art. In a conventional arc spray gun, an electric arc is utilized to melt a metallic material so that the molten metal may be sprayed onto a surface, such as a steel plate or other object, in order to form a desirable coating on the surface. Typically, two metal wires serve as consumable electrodes between which the electric arc is established. Simultaneously, compressed gas is injected into the arc zone region behind the metal wires. The compressed gas atomizes the molten metal created by the arc and propels the metal particulate onto the surface.
In a conventional arc spray gun, two metal wires are guided through the gun along respective paths. The wires exit the gun at a location often referred to as the arc spray head. The arc spray head includes the gun structure where the wires exit the gun and also may include the space near the actual gun sturcture. At the arc spray head the path of the two wires converge and intersect. An electrical potential difference established across the two wires causes an electric arc to occur between the wires at the area at which the wire paths intersect. The heat generated by the arc melts the ends of the two wires, and a gas nozzle positioned at the arc spray head directly behind the intersection of the wire path directs a stream of high velocity gas which impinges upon and atomizes the molten metal. The gas stream then carries the atomized metal particles, or droplets, away from the arc zone and propels them towards the surface to be coated.
Some arc spray guns have utilized a secondary gas stream to divert the atomized metal spray a certain angle in order to direct the spray into a small or confined area. Other guns have employed a secondary gas stream interacting with the primary stream to provide somewhat controlled atomization and flow of the spray at least within the area of the arc spray head. An example of the latter type of an electric arc spray gun is described in U.S. Pat. No. 4,492,337 the disclosure of which is incorporated by this reference.
While conventional electric arc spray devices provide an effective way of coating a surface, they tend to be somewhat inefficient in that a substantial quantity of the material consumed is not deposited on the intended surface. Often 40% or more of the material is lost through overspray and dust formation. Also, due to an inability to accurately concentrate and direct the spray of molten metal droplets, it has been difficult to achieve a uniform thickness of the coating in all areas of the coated surface. Consequently, it was necessary to use a large excess of coating material to ensure that all areas of the surface had an adequately thick coating to premit further finishing operations. Even when a relatively uniform thickness of coating could be created, the surface tended to be rather coarse, again requiring extensive finishing. These problems further exacerbated the inefficiency by requiring that a substantial amount of deposited coating material be machined away to provide a surface with the requisite dimensional tolerances and finish.
A further problem with conventional arc spray guns has been that they are not versatile and do not provide effective means for adjusting flow rate, particulate size, and deposit patterns to best satisfy a particular application.
It would be desirable to provide a versatile electric arc spray device that produced a concentrated and well directed pattern of molten metal droplets, and a coating with finer surface finish.